1. Field of the Invention
This invention relates to the obtaining of contaminant samples which have been deposited along the interior surface of a pipe; and more particularly it concerns a novel method and apparatus for applying a large area swab to the inner surface of a pipe so that a representative sample of the contaminant can be recovered from the pipe without interfering with the flow of fluid through the pipe.
2. Description of the Related Art
Large diameter pipes, such as gas mains, are often required to convey gasses which may contain harmful contaminants such as polychlorinated biphenyls (PCBs) or Benzine. These contaminants may precipitate out of the gas stream and become deposited along the interior service of the pipe. Thereafter, when clean gas passes through the pipe, it comes into contact with the contaminant deposits so that it may also become contaminated.
It is therefore important, at any given time, to know whether sufficient contaminants have become deposited long the inner surface of a pipe such that they would be likely to cause further contamination of clean gas passing through the pipe. It is also important not to interrupt gas flow through the pipe or otherwise disrupt its operation while inspecting its inner surface for contaminants. This becomes a difficult problem in that in order to obtain an accurate indication of the condition of a pipe's inner surface, a minimum area of the surface, usually at least four square inches (25 square centimeters), must be examined; and to expose this much of a pipe's interior while maintaining normal gas flow through the pipe is especially difficult.
U.S. Pat. No. 5,269,968 discloses a technique for removing PCBs from the contaminated inner surface of a pipe by means of a swab sampling technique in which the pipe is first cut into pieces to expose its inner surfaces.
U.S. Pat. No. 5,686,674 discloses the use of a sensor which is dragged through the interior of a pipe to sense radioactive contamination along the inner surface of the pipe.
U.S. Pat. No. 4,919,892 discloses the use of a perforated housing which is positioned in the path of fluid flow in a pipe to absorb contaminants from the fluid passing through the pipe.
U.S. Pat. Nos. 5,463,908 and No. 5,531,130 relate to the use of probes which are inserted into pipes to measure conditions in the fluids which flow through the pipes.
U.S. Pat. Nos. 3,842,864, 3,910,298 and 5,400,826 show the use of inflatable balloons inside of pipes to stop the flow of fluid in the pipe.
U.S. Pat. No. 1,636,243 shows the use of an inflatable balloon to press a pad against the interior of a pipe joint to prevent sealant, which is being applied to the exterior of the pipe joint, from leaking into the pipe.
A satisfactory method or means for effectively ascertaining the contamination of an inner pipe surface while fluids are flowing normally through it appears not to be disclosed in the prior art.